Display devices have typically used cathode-ray tubes (CRT). Presently, much effort has been made to study and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDP), field emission displays, and electro-luminescence displays (ELD), as a substitute for the CRT. LCD devices have advantages over the other flat panel displays, some of the advantages are high resolution, light weight, thin profile, compact size, and low power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other. A voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
Because the LCD device is a non-emissive type display device, a backlight is needed to supply the non-emissive type display device with light. A CCFL (cold cathode fluorescent lamp) or an EEFL (external electrode fluorescent lamp) has been previously used. Recently, a LED (light emitting diode) is used because it has small size, low power consumption and high reliability.
FIG. 1 is an exploded perspective view illustrating an LCD device according to the related art.
Referring to FIGS. 1 and 2, in the related art LCD device, a backlight unit 30 and a liquid crystal panel 10 are sequentially disposed over a bottom case 50. A main supporter 40 has a rectangular frame shape and supports the backlight unit 30 and the liquid crystal panel 10. The main supporter 40 is combined with the bottom case 50.
A driving circuit is connected to the liquid crystal panel 10 through a FPC (flexible printed circuit) film 12. A top case 60 is disposed on the top of the liquid crystal panel 10. The top case 60 has a rectangular frame shape. The top case 60 presses and fixes a peripheral portion of the liquid crystal panel 10 and is combined with the main supporter 40 and the bottom case 50.
The backlight unit 30 includes a plurality of LEDs 33, a reflection sheet 34, a diffusion plate 36, and optical sheets 38 such as a prism sheet and a diffusion sheet. The LEDs 33 are arranged on a plurality of MCPCBs (metal core printed circuit boards) 32. The MCPCBs 32 are arranged in parallel on the bottom case 50 and are connected through a conductive line 39 to be supplied with a power for the LEDs 33.
The reflection sheet 34 has a plurality of through holes 35. The through holes 35 correspond to the LEDs 33. The reflection sheet 34 covers the MCPCBs 32 with the LEDs 33 passing through the through holes 35 and protruding. A pair of side supporters 26 are coupled with the reflecting sheet 34, form a space to set up the backlight unit 30, and function to prevent light from leaking outward.
Light emitted from the LEDs 33 and reflecting on the reflection sheet 34 is diffused through the diffusion sheet 35 first, then becomes uniform plane light having high quality through the optical sheets 38, and then is supplied to the liquid crystal panel 10. The diffusion plate 36 has a thickness of about 1 to 4 mm (millimeters).
As size of the LCD device increases, size and weight of the diffusion plate 36 increases. This weight increase causes middle portion of the diffusion plate 36 to sag. Further, this is against recent trend of decreasing the weight of the LCD device.